Birgeria

Birgeria is a group of ancient carnivorous fish that lived in the oceans during the Triassic period. These fish were found all over the world, with fossils discovered in places like Madagascar, Spitsbergen, Germany, Switzerland, Italy, Slovenia, China, Russia, Canada, and Nevada in the United States. The earliest fossils of Birgeria come from layers of rock in East Greenland that date back to the very start of the Triassic period, right after a big event called the Permian-Triassic mass extinction. Birgeria lived until the end of the Triassic period, going extinct during another big event known as the Triassic-Jurassic mass extinction.

At first, scientists thought one of these fish belonged to a different group called _Saurichthys_. But after studying it more, a scientist named Erik Stensiö decided it was different enough to deserve its own group. He named this new group after his friend Birger Sjöström, who had gone with him on a trip to the Arctic island of Spitsbergen (Svalbard) in 1915.

Systematics

Birgeria is the only genus of the family Birgeriidae and order Birgeriformes. Other fish groups like Psilichthys, Ohmdenia and Brazilichthys were once thought to be related, but they are actually far away from Birgeria. This family was first described in 1937. The first detailed description of Birgeriidae was done in 1949. These fish first appeared in the very early Triassic period in Greenland and disappeared by the late Triassic period. They were most common during the early to middle Triassic.

In many studies, Birgeria is closely related to the Saurichthyiformes. Together, they are often linked to groups like sturgeons and paddlefish. However, some studies suggest they might not be closely related to these fish and could belong to an older group of fish called Actinopterygii. Some species of Birgeria are not fully known, and one species' original samples are lost. With around eight known species, Birgeria was less common than another fish group called Saurichthys. Fossils of unknown species have been found in Canada, Bolivia, Luxembourg, and Saudi Arabia.

Appearance

Birgeria had very few scales, mostly only on the upper part of its tail fin and the back part of its tail base. The scales that were present were small and diamond-shaped.

Its tail fin was large and split deeply in the middle. The top and bottom fins were placed at the same spot toward the back of its body. The eyes were positioned toward the front of its head, and it had long jaws with many sharp teeth.

Ecology

Birgeria was a top hunter among fish from the Triassic period, living together with another fish called Saurichthys.

Most Birgeria fish grew longer than 1 meter (about 3.3 feet), with some reaching up to 2 meters (about 6.6 feet) or more. Some of the biggest types lived in the early Triassic, such as Birgeria aldingeri from Spitsbergen and Birgeria americana from Nevada, United States. They were among the first large hunters to appear after a big event called the Permian-Triassic mass extinction.

Scientists once thought a Birgeria fossil from Madagascar might have carried baby fish inside, but this idea was later dropped. It now seems more likely that these were actually small fish that Birgeria had eaten. Unlike Saurichthys, Birgeria probably did not give birth to live young. This idea is supported because no fossils showing special organs for this have been found.

From its body shape, scientists believe Birgeria was a fast swimmer in the open ocean. Because there are not many fossils of it, it likely lived far from shore.